Vehicle emissions are highly regulated to keep the output of environmentally-harmful exhaust emissions to a minimum. If vehicle exhaust is left untreated, the levels of pollutants would far exceed the emissions standards set by the Environmental Protection Agency and the states. The major regulated pollutants include carbon monoxide (CO), nitrogen oxide compounds (NOx), and unburned hydrocarbons (CxHy).
To meet these standards, vehicles include exhaust treatment systems, which generally include two stages of catalytic converters. An example of such an exhaust treatment system is illustrated in FIG. 1, which is a block diagram of an underbody of a vehicle 10 according to the prior art. The vehicle 10 includes engine 100, first catalytic converter 110, second catalytic converter 120, and muffler 130, which are in fluid communication with one another through pipe or conduit 140. In operation, the engine 100 generates exhaust, which travels through conduit 140 to first catalytic converter 110, second catalytic converter 120, muffler 130, and then exits through tail pipe 150. The first catalytic converter 110, known in the industry as the “light off” catalytic converter, is disposed close to engine 100 to treat exhaust emissions while engine 100 is cold (e.g., below 600° F.), such as during a cold start of engine 100. The second catalytic converter 120, known in the industry as the “underbody” catalytic converter, is disposed further away from engine 100 underneath the passenger compartment of the vehicle 10. The second catalytic converter 120 typically does not meaningfully contribute to exhaust treatment until the engine 100 heats up (e.g., above 650° F.), which typically occurs when the engine 100 becomes loaded.
A problem with existing emissions control systems is that the emissions output of carbon monoxide (CO) and hydrocarbons (CxHy), e.g. from partially-combusted fuel, is high when the exhaust temperature is low, such as while the engine warms up from a cold start. It would be desirable to have an emissions control system that more effectively treats CO and CxHy compounds while the engine and exhaust heat up from a cold start.